The present invention relates to power amplifiers.
Class-D amplifiers are power amplifiers having an input stage and an output stage. The output stages are conventionally operated in a switching mode. This means that the output stage is either switched on or switched off.
Conventionally, pulse width modulation is used in class-D Power Amplifiers. The (analogue digital) input signal is converted into a periodic sequence of pulses having a predetermined pulse frequency. The pulse width represents the amplitude of the input signal at one point in time. The pulse frequency is chosen to be at least twice as large as the maximum frequency of the input signal. Typically, the pulse frequency is ten or more times higher that the highest frequency of the input signal.
The pulse width modulated signal is input to high power switching device, which generates a high power replica of the pulse width modulated signal. This amplified pulse width modulated signal is fed to an integrator, which removes the high-frequency switching components of the PWM signal and recovers the input signal. In particular, class-D Power Amplifiers may be used for sound amplification. For this application, the output is fed to a loudspeaker. Class-D Audio amplifiers typically use switching frequencies greater than 100 kHz.
Conventionally, differential pulse width modulation is used in conventional Class-D Amplifiers. In this case, the differential pulse width modulator uses two modulated output signals for representing an input signal. The difference between the output signals is a pulse modulated signal encoding the input signal. Differential amplification has the advantage that interference on a single pulsed signal is cancelled in the case of differential amplification. However, energy consumption is increased, since two output signals instead of one output signal are generated. Consequently, the high frequency noise may cause the connected loudspeaker cable to transmit electromagnetic radiation. In this case, the loudspeaker cable acts as an antenna. This electromagnetic noise is unwanted, since it may affect electronic devices.
For these and other reasons, there is a need for the present invention.